Production of alkenylpyrroles



Jan. 15, 1 946. c. R. WAGNER l 2,393,132

' PRODUCTION OF ALKENYLPYRROLES Filed Nov. '26, 1943 www l U o |UL1 N 1 tIOiVNOLLOVBd INVENTOR c.. R. WAGNER Patented 15, 1946 UNiTEo STATES PATENT VOFFICE PRODUCTION oF aLnENrLrranoLas Cary Wagner, Utica, Ohio, assigner to Phillips A.. Petroleum Company, a corporation of Delaware Application November 26, 1943, Serial No. 511,895

' y Berichte, 1912, v01. 45, page 745.)

V Claims.

The present invention relates to the productionA of alkenylpyrroles and, more particularly, to the (Cl. ZBO- 313) oi the resulting ethylpyrrole to vinylpyrrole. 'Ihe invention also pertains to a continuous process for the production of vinylpyrrole from pyrrole and ethylene.

N-vinylpyrrole or 1-vinylpyrrole, as well as N-ethylpyrrole, or l-ethylpyrrole, are known compounds. N-vinylpyrrole, which is reported to have a boiling point of 122 C., was prepared by the reaction of pyrrole with acetylene in the presence of potassium hydroxide at a temperature of 180 to 190 C. and a pressure of 20 atmospheres (Reppe and Keyssner, U. S. Patent No. 2,066,160; see also German Patent No. 618,120, British Patent No. 438,281 and French Patent No. 790,467). The

only other reported method which is said to be capable of producing the compound comprises the reaction of pyrrole with a vinyle halide or ethylene halide in the presence of an alkaline compound (Reppe, Keyssner and Nicolai, U. S. Patent No. 2,153,993). The only other N-alkenylpyrrole which is reported is-N-allylpyrrole or l-allylpyrrole, which is stated to have a, boiling point of 105 C. at a pressure of 48 millimeters of mercury. It was prepared by heating potassium pyrrole with allyl bromide in ether (Ciamician and Dennstedt, Berichte, 1882, vol. 15, page 2581; Gazzetta chim. ital., 1883, vol. 13, page 17.)

Several C-alkenyl-substituted pyrroles have been reported. 2-allylpyrrole or alpha-allylpyrrole, which is stated to have a boiling point of 82 to 83 C. at a pressure of 24 millimeters of mercury, was prepared together with 2,5-diallylpyrrole by treatment of pyrrole magnesium bromide with allyl bromide in ether (Hess, Berichte, 1913. vol. 46, page 3127). On reduction of indolizine .(pyrrocoline) with sodium and alcohol, 2(1,3

butadienyD-pyrrole was obtained. This product had a boiling point of 198 to 199 C. (Scholtz,

N-ethylpyrrole or l-ethylpyrrole has been obtained by heating potassium pyrrole with ethyl iodide (Ljubawin, Berichte, 1869, vol. 2, page 101;

Bell, Berichte, 1878, vol. 11, page 1810; Zanetti, Gazzetta chim. ital., 1889, vol. 19, page 90; Berichte, 1889, vol. 22, page 660), It has been obtained by heating the ethylamine salts of mucic acid and saceharic acid, respectively (Bell, Berichte, 1876, vol. 9, page 936; ibid., 1877, vol. 10,

page 1862; Bell and Lapper, Berichte, 1877, vol.

10, page 1962), and also -by heating l-ethylpyrrole-Z-carboxylic acid by itself or 'with dilute acids (Bell, Berichte, 1877, vol. 10, page 1862; Bell and Lapper, Berichte, 1877, vol. 10, page 1961). N-ethylpyrrole is reported tohave a boiling point in the range of 129 to 131 C. Other N-alkylsubstituted Pyrroles which are known are N-propylpyrrole and N-isoamylpyrrole, whose boiling points are 145.5 to 146.5 C. at a pressure of 755.8 mm. of mercury and 180 to 184 C., respectively.

C-alkyl-substituted pyrroles, in which the sub-- stituent is present on the carbon atoms of the ring, are also known and have been prepared and studied more extensively than the N-alkyl-substituted'isomers. 2-ethylpyrrole or alpha-ethylpyrrole, for example, which is an oil having a boiling point of 163 to 166 C. at atmospheric pressure and 66 to 68 C. at a pressure of 17 to 18 mm. of mercury, was obtained by passinga mixture of vapors of pyrrole and ethyl alcohol over zinc dustat-270" to 280 C. (Dennstedt, Berichte, 1890, vol. 23, page 2563). It has been obtained together with other products by heating potassium pyrrole with an excess of ethyl iodide (Ciainician and Zanetti, Gazzetta chim. ital., 1889, vol. 19, page Zanetti, Gazzetta chim. ital., 1889, vol. 19, page 290; ibid., .1891, vol. 211, page248; Berichte, 1889, vol. 22, page 2517). 2-ethylpyrrole has also been obtained by treating a mixture of pyrrole and paraldehyde with zinc chloride and subsequent heating of the reaction product (Denn'stedt and Zimmermann, Berichte, 1886, vol. 19, page 2190) It has also been obtained by heating pyrrole magnesium bromide with ethyl iodide in ether (Oddo and Mameli, Gazzetta chim. ital., 1914, vol. 441, 168), and with ethyl bromide in 'ether (Hess and Wissing, Berichte, 1914, vol. 47,

page 1424; Hess, Wissing and Suchier, Berichte, 1915, vol. 48, page 1883).

N-alkyl-substituted pyrroles are readily isomerized to C-alkyl-substituted pyrroles by heat. This isomerization occurs at approximately 200 C. or higher. For example, N-methylpyrrole (l-methylpyrrole) is isomerized to 2-methy1-pyrrole (a C-methylpyrrole) by passing it through a tube heated until it glows-weakly (Pictet, Berichte, 1904, vol. 37, page 2793). The change is from a compound of a lower boiling point to one of higher senation of the alkyl-substituted pyrroles to alkenyl-substituted pyrroles.

It is another object of the present invention to provide a continuous process for the production of alkenvlpyrroles from oleilns and pyrrole which involves the alkylation of pyrrole with an olefin and dehydrogenation of the resulting alkylpyrrole.

Other objects and advantages of the invention, some of which are referred to speciiically hereinafter, will be apparent to those skilled in art to which the invention pertains.

According to the present invention, alkenylpyrroles are produced from pyrrole and an olefinby alkylation of pyrrole with an olefin and dehydrogenation of the resulting alkylpyrrole. 2-vinylpyrrole is produced, for example, by aikylation of pyrrole with ethylene to produce an ethylpyrrole, which is thereafter dehydrogenated to 2vinylpyrrole. The process is preferably conducted in a continuous manner as hereinafter more specifically described. The alkylation is efiected in the presence of catalysts whereas the dehydrogenation may be catalytic, which is preare ,formed in the dehydrogenation may be discharged i'rom the iractionator through vent Il. In the iractionator a separation is made between 2-vinylpyrrole. which is removed through a disferred, or simply a noncatalytic thermal dehydro- I to an alkylator 2. This alkylator contains a silica-alumina. catalyst or other suitable alkylation catalyst. The pyrrole is charged in substantial excess over that which would be required for its complete monoalkylation by the ethylene charged.

. The mixture after passing through alkylator 2 is then passed through conduit 3 to fractionator 4. Uncombined ethyleneis discharged through vent 5 or is returned through conduit E to alkylator 2. In fractionator l a separation is also made between pyrrole, ethylpyrrole and any polyethylated pyrroles. The unethylated pyrrole passes back through line 6 to alkylator 2. Ethylpyrrole passes through conduit l' to a furnace 8. Polyalkylated pyrroles, which accumulate at the bottom of fractionator 4, are recharged to alkylator 2, where they are partially dealkylated inthe presence of the excess of pyrrole. V

The ethylpyrrole is heated in furnace 8 to a suitable temperature for dehydration and is then passed through conduit 9 to a dehydrator I0 which is charged with a suitable dehydration catalyst. After being subjected to dehydrogenation, the product is passed through conduit I l to a fractionator I2. In the event that noncatalytic dehydrogenation is to be used, dehydrogenator I8 is omitted and the desired thermal dehydrogenation is effected in furnace 8, which is a 70 tube furnace, or other suitable pyrolysis apparatus, for example, a bath of lead .or other molten metal, and the product is charged to fractionator hydrogen and any low-boiling products which sulfur.

charge outlet I5, and Z-ethylpyrroie. which is the overhead and is returned'to furnace 8 through conduit Il for further dehydrogenation.

To prevent polymerization of 2-vinylpyrrole during the distillation in fractionator I2, it is generally desirable to add an inhibitor such as sulfur to the material undergoing distillation. The inhibitor may be added at i8. If sulfur is used as inhibitor it will remain in the bottoms in fractionator I2 and will be discharged through conduit I8 with 2-vinyl pyrrole. For the purpose of removing the inhibitor 'in the 2-vinylpyrrole in conduit I 5 a flash still I 'I may be provided. The inhibitor is discharged through outlet I8 from flash still I1 and the overhead vinylpyrrole is recovered at outlet I9. Polymerized vinylpyrrole and higher-boiling residual materials may be charged through line 28 to furnace 8 for further pyrolysis. The recovered inhibitor, if relatively free from contaminants, may be reused by charg ing it to inlet I6 at the top of fractionator I2.

The foregoing process is typical and by suitable substitution may be used for the production of all-renylpyrroles generally from oleiins and pyrrole.

Olenns which may be used for the alkylation to produce the corresponding alkyl-substituted pyrroles are ethylene, propylene, 1butene, 2-butene, isobutylene (2-methyl-1-propene), pentenes, etc.

Instead of starting with pyrrole, substituted pyrroles may be used. For example, 3-methylpyrrole may be further alkylated with ethylene according to the process of the invention and then dehydrogenated to give 2-vinyl-3-methylpyrrole or some other isomer thereof. If one starts with a pyrrole substituted with an ethyl or higher alkyl group this group may be dehydrogenated in the subsequent dehydrogenation step.

Sulfur has been disclosed herein as an inhibitor y of the polymerization of vinylpyrrole and other allrenylpyrroles. .It may be used both in the dis. tillation as described herein, being introduced at the top of fractionator I2, and to inhibit the polymerization of the product on storage, in which event its removal by distillation before use may be required. However, other polymerization inhibitors, for example, alkyl-substituted catechols and similar suitable alkyl-substituted phenols, may be used instead of or in conjunction with The amount of inhibitor to be used is largely dependent upon the effectiveness of the inhibitor and upon the degree of inhibition that is desired. Normally, in distillation, to inhibit polymerization, an amount of sulfur within the range of 0.1 to 1 per cent by weight of the material in the column is generally sumcient, although more may be used if desired.

Instead of using a continuous process as dethe separation in fractionator I2, is contemplated and is desirable because of the increased tendency possible.

for polymerization of the alkenylpyrrole as the temperature is raised. Because the boiling points of alkylpyrroles and the corresponding allrenyl-f` Boiling points (C.) of substituted pyrroles N-ethyL. 129131 N-vlnyl 122 Z-ethyl 163-166 N-propyl M55-146.5

. N-allyl 105/48 mm. Z-propyl 176179 2-al1yl 82-83/24 mm. 2(l,3butadienyl) 198-199 The foregoing boiling point ranges are those reported inthe literature and are the limits within which all the reported samples boiled, that is, they are not the boiling range of any particular Patents No. 2,129,649; 2, 129, 732 and 2,129,733), Chapman and Hendrix (Serial No. 371,209, filed December 21, 1940), and Hachmuth (Serial No. 370,558, led December 17,'1940). A .suitable catalyst of this class may be prepared by precipitation of hydrous silica gel, by the addition of a. sodium silicate solution to a solution of sulfuric acid. The resulting gel 'is washed with water and then partially dried. The partially dried silica gel is then washed again with water and treated with a solution of aluminum sulfate and againwashed. 'I'he treatment with aluminum sulfate and washing .with water are -resample; N-ethylpyrrole, for example, has been granular solid supporting material are also suitable. Solid catalysts of this type may and preferably are used under vapor-phase conditions of operation and generally Within the temperature range of approximately 400 to approximately 700 F. However, alkylation in the liquid phase at lower temperatures may be adopted with catalysts such as phosphoric acid, sulfuric acid,

anhydrous hydrogen fluoride, and hydrogen.

fluoride containing boron fluoride. VWhen using the latter acid catalysts, provision must be made for maintaining sulcient pressure to obtain liquid-phase reaction conditions and also for decomposing any acid compounds which are formed in the reaction. Thus, on alkylating pyrrole with ethylene in the presence of a large excess of hydrogen iiuoride, some of the pyrrole will be converted to pyrrole hydrofluonde and perhaps ethylpyrrole hydrofluoride, although alkylation with ethylene at low temperatures favors formation of an N-ethylpyrrole, in which event, decomposition of such salts, generally by means of alkali, will be required before proceeding with the dehydrogenation thereof.

Suitable catalysts of the silica-alumina type are those prepared by subjecting partially dried silica gel to the action of a hydrolyzable salt of a metal of group III-B or IV-A of the periodic system.v Such catalysts are described by Gayer (Industrial and Engineering Chemistry, 1933,

volume 25, page 1122), Perkins et al. (U .S. Patent No. 2,107,710), McKinney (U. S. Patents No.

2,142,324 and 2,147,985), Fulton and Cross (U. S.

-peated until suillcient aluminum compound is adsorbed on the gel and the material is thereafter dried, preferably ata temperature not substantially in excess of approximately 225 F.

Catalysts suitable for the vapor-phase dehydrogenation of alkylpyrroles t'o alkenylpyrroles include chromium oxide and molybdenum oxide, which may be used alone or supported on suitable catalystcarriers. A preferred catalyst is unglowed chromium oxidesupported on alumina or bauxite.- Other suitable catalysts are thorium oxide on alumina. An especially advantageous catalyst is one containing chromium oxide together with calcium oxide or other alkalineearth-metal oxide and/or an alkali-metal oxide or hydroxide, or one such as is described in Corson and Cox Patent No. 2,311,979. Other suitable chromium oxide catalysts are described in the patents of Morey and Frey (No. 2,270,887). Matuszak (No. 2,294,414), Grosse (No. 2,172,534), Huppke and Frey (No. 1,906,383 and 2,098,959), and Visser and Engel (No. 2,249,337)

The dehydrogenation ispreferably conducted under reduced pressure. This may be accomplished by diluting the reactantsv with an inert gas such as nitrogen, steam, or carbon monoxide.

The temperatures which are used for the dehydrogenation are generally within the range of approximately 800 to approximately l200 F. and preferably between 900 and 1100 F. As previously stated, low dehydrogenation temperatures may be used when catalysts are employed to facilitate the reaction.

The reaction mixture which is charged to the alkylator should contain a molecular excess of tion reaction conditions. With ethylene, for example, a higher molecular ratio of pyrrole to ethylene would be more desirable than' with isobutylene.

Aslan example of the practice of the process of this invention, the following preparation of 2-vinylpyrrole, which is a batchwise operation, is cited: Pyrrole and ethylene are charged to a chamber containing a silica-alumina catalyst prepared according to the general method hereinabove described. The molecular ratio of pyrrole to ethylene is 5 to 1 and the materials are heated to such temperature that the temperature of the catalyst bed is approximately 500"v F. The products are condensed and then fractionally distilled. The pyrrole (boiling range approximately to 130 C.) is separated from the ethylpyrroles (boiling range approximately to. C.), which probably includes N-ethylpyrrole and 2-ethylpyrrole.

- Ethylpyrrole as obtained above is then heated condensed and distilled fractionally in a 6-foot glass column packed with` glasshelixes to separate theundehydrogenated 2ethylpyrrole from the 2-viny1pyrrole.

Substantial yields of ethylpyrrole and 2vinyl pyrrole are obtained, although the conditions specified in the foregoing example are not to be understood to be optimum conditions.

In addition to 2-vinylpyrrol, the crude product from the reaction of pyrrole and ethylene contains vinylpyrroles in which the vinyl group is present on the nitrogen atom and on other carbon atoms of the pyrrolean'ucleus. Furthermore, when propylene and higher oleflns are used as alkylating agents the product is a mixture of isomers in which the 2 or alpha alkenyl isomer is predominant and the 3 or beta allrenyl isomer is second in predominance: together with N-alkenylsubstituted pyrroles, although this will depend to a large extent on the specific reaction condi'- tions used. It is not to be understood, therefore, that the invention is limited otherwise than as described or claimed.

2-vinylpyrrole and other allrenylpyrroles which can be obtained by the process of the present invention may be readily polymerized to products which are useful as plastics and which can be molded under heat and pressure and which are thermoplastic as contrasted to thermosetting plastic materials. They are also useful in the form of copolymers with 1,3-butadiene (erythrene), isoprene (2-methyl1,3butadiene) and piperylene (1,3-pentadiene) respectively, as synthetic rubbers, namely products which possess a high elasticity and resemble naturalV rubber in other respects. Such copolymers even surpass natural rubber in some properties.

I claim:

1. A process for the production of an alkenyllpyrrole which comprises alkylation of pyrrole with 'an olefin hydrocarbon to produce an alkylpyrrole and dehydrogenation of the resulting alkylpyrrole to an alkenylpyrrole. v

2. A process as defined in claim 1 in which the oleiln hydrocarbon is an olen hydrocarbon having less than six carbon atoms per molecule.

7. A process as dened in claim 5 in which the dehydrogenation catalyst is a catalyst containing .chromium oxide.

8. A continuous process for the production of an alkenylpyrrole which comprises passing a mixture of an oien hydrocarbon and pyrrole comprising pyrrole in molecular excess into contact with a solid alkylation catalyst at a temperature within the range of approximately 400 to approximately '700 F., recovering unreacted pyrrole and recharging it together with additional amounts of olen hydrocarbon to the alkylation catalyst, separating alkylated pyrrole from the alkylation reaction product and subjecting it to dehydrogenation in the presence of a dehydrogenation catalyst at a temperature within the range of approximately 800 toapproxlmately 1200 F., separating undehydrogenated alkylpyrrole from the product 'of the dehydrogenation reaction and recharging it to the dehydrogenation catalyst, and separating and recovering alkenylpyrrole from the'product of the dehydrogenation reaction.

9. A process for the production o! 2vinylpyr role which comprises alkylation of pyrrole with ethylene to produce -ethylpyrrole and dehydrogenation of the resulting 2-ethylpyrrole to 2-vinylpyrrole.

10. A process for the production of Z-ethylpyrrole which comprises alkylation of pyrrole with ethylene.

V11. A process for the `production of Z-Vinylpyrrole which comprises dehydrogenation of 2-ethyl' pyrrole.

12. A process for the production of 2vinylpyrrole which comprisesalkylation of pyrrole with ethylene in the presence of a solid alkylation catalyst at a temperature within the range of approximately 400 to approximately r100 F. to

40 produce Z-ethylpyrrole and dehydrogenation of 3. A process for the production of an alkylpyrf role which comprises alkylation of pyrrole with an. olefin hydrocarbon to produce an alkylpyrrole.

4. A processior the production oi' an alkenylpyrrole winch comprises dehydrogenation ci an alkylpyn'ole.

5. A process' for the production of an allienyl-l the 2ethylpyrrolein the presence oi' a solid dehydrogenation catalyst at n temperature within the range of approximately 800 to approximately l200 F. to produce 2-vlnylpyrro1e.

13. A process as deilned in claim 12 in which the alkylation catalyst is a catalyst oi the silicaalumina type.

14. A process as-delned in claim 12 in which the dehydrogenation catalystk is a catalyst containing chromium oxide.

15. A continuous process for the production oi 2-vinylpyrrole which comprises passing a mixture of ethylene and pyrrole comprising pyrrole in molecular excess into contact with a solid alkylation catalyst at a temperature within the range of aD- proximately 400 to approximately 700 F., recovering unreacted pyrroie and recharging it together with additional amounts oi ethylene to the alkylationcatalyst, separating ethylated pyrrole from the alkylation reactionproduct and subecting it to dehydrogenation in the presence of a dehydrogenation catalyst at a temperature within the range of approximately 800 to approximately 1200 F., separating undehydrogenated ethylpyrrole from the product of the dehydrogenation reaction and recharging it to the dehydrogenation catalyst, and separating by fractional distillation in the presence of an inhibitor of polymerization and recovering 2-vinylpyrro1e from the product of the dehydrogenation reaction.

CARY .R. WAGNER. 

